The invention relates to a chain drive system having parts sliding on each other with less friction resistance and wear so as to increase in durability, prevent secular deteriorations in system performance and obtain, when used to transmit the rotation of a crankshaft to a valve driving camshaft in an internal combustion engine, improvements in engine performance and fuel efficiency.
Japanese Laid-Open Patent Publication No. 6-264993 discloses one type of chain drive system to transmit the rotation of a crankshaft to a pair of valve driving camshafts in an internal combustion engine, which includes a crankshaft sprocket connected to the crankshaft, camshaft sprockets connected to the respective camshafts, a chain looped over the crankshaft sprocket and the camshaft sprockets, a chain guide that guides the chain in a proper chain drive direction and a chain tensioner unit that controls a tension in the chain hydraulically. In the above type of chain drive system, either a roller chain or a silent chain is usable, as proposed in Japanese Laid-Open Patent Publication No. 11-190406.